In recent years, metallocene compounds have been known as homogeneous catalysts for olefin polymerization. With regard to polymerizing olefins (in particular, polymerizing α-olefins) by use of metallocene compounds, since isotactic polymerization has been reported by W. Kaminsky et al., many studies have been conducted for improvement of stereoregularity and polymerization activity (Non-Patent Document 1).
It is known, in α-olefin polymerization by use of metallocene compounds, that the stereoregularity and molecular weights of olefin polymers greatly vary by the introduction of substituents to the cyclopentadienyl ring ligands of the metallocene compounds or by the crosslinking the two cyclopendienyl rings.
For example, when metallocene compounds having a ligand in which a cyclopentadienyl ring and a fluorenyl ring are crosslinked is used as a polymerization catalyst, in terms of the stereoregularity of polymers, dimethylmethylene(cyclopentadienyl)(fluorenyl)zirconium dichloride affords syndiotactic polypropylene (Non-Patent Document 2), dimethylmethylene(3-methylcyclopentadienyl)(fluorenyl)zirconium dichloride, which has a methyl group attached to the 3 position of a cyclopentadienyl ring, affords hemi-isotactic polyprolylene (Patent Document 1); and dimethylmethylene(3-tert-butylcyclopentadienyl)(fluorenyl)zirconium dichloride, which has a tert-butyl group attached to the 3 position of a cyclopentadienyl ring, affords isotactic polyprolylene (Patent Document 2).
In modifying these metallocene compounds, it is possible to obtain high melting points, an indicator of the stereoregularity of a polymer, and to obtain high molecular weight. Also, it is possible to produce a polymer with a high melting point and a sufficiently high molecular weight.